Cavitary histoplasmosis has been experimentally produced in rhesus monkeys infected intratracheally. Previous observations have suggested that delayed hypersensitivity (cellular immunity) to the organism is responsible for the pulmonary cavitation process and that the presence of circulating antibodies against the organism can block the development of cavities. Passive immunization experiments (immune cells and antibodies) have confirmed the original observations in that cavitation was enhanced by passive administration of immune T-cells and cavitation was blocked by passive administration of immune globulin. BIBLIOGRAPHIC REFERENCES: Bauman, D.S. and C. D. Smith, 1975. Comparison of Immunodiffusion and Complement Fixation Tests in the Diagnosis of Histoplasmosis. J. Clin. Microbiol. 2:77-80. Bauman, D.S. Significance of the Immunodiffusion Test in the Diagnosis of Opportunistic Mycoses. In: Proceedings of the Second International Symposium on Opportunistic Fungal Infections, E. W. Chick, Et al., eds. C. C. Thomas and Co., Springfield, Illinois, 1975.